Differential detection for surface plasmon resonance sensor and method

Abstract

A differential measurement design employing two nearly collinear optical beams provides surface plasmon polariton resonance (SPR) sensors and a corresponding method of increased dynamic range and signal to noise ratio. The differential measurement device and method based on wavelength interrogation, employs a single incident polarization state, and is combined with a 2-D nanohole array for operation at near-normal incidence, where this approach offers a decrease in the measurement time.

What is claimed is: 
     
       1. In a surface plasmon resonance sensor having a metal-dielectric interface formed by microfluidic channels integrated with metal-dielectric layer chips, the method comprising:
 imaging a pair of collimated laser beams at different angles of incidence onto substantially the same spot on a metal nanohole array sample at the metal-dielectric interface to excite surface plasmons on the array sample and forming a pair of transmitted laser beams emerging from the array sample; 
 forming a pair of parallel laser beams corresponding to the pair of transmitted laser beams; 
 obtaining a pair of device transfer function (DTF) signals from the pair of parallel laser beams, where each respective DTF signal has a different angle of incidence and an intensity peak at a different wavelength relative to a reference wavelength; 
 calculating a difference signal from the pair of DTF signals, where the difference signal has positive and negative values about a zero crossing axis which are representative of transmittivity relative to wavelength and where a resulting shift in the location of the difference signal at the zero crossing axis represents a changing refractive index of the dielectric at the metal-dielectric interface. 
 
     
     
       2. The method of  claim 1  where the resonance sensor is in a closed loop configuration. 
     
     
       3. The method of  claim 2  including obtaining the DTF signals at FWHM (Full Width Half Maximum) values. 
     
     
       4. The method of  claim 3  where the array sample is a grating array. 
     
     
       5. A surface plasmon resonance sensor having a metal-dielectric interface formed by microfluidic channels integrated with metal-dielectric layer chips, the sensor comprising:
 laser means for generating and imaging a pair of collimated laser beams at different angles of incidence onto substantially the same spot on a metal nanohole array sample at the metal-dielectric interface to excite surface plasmons on the array sample and forming a pair of transmitted parallel laser beams emerging from the array sample; 
 processor means for obtaining a pair of device transfer function (DTF) signals from the pair of parallel laser beams, where each respective DTF signal has a different angle of incidence and an intensity peak at a different wavelength relative to a reference wavelength and for calculating a difference signal from the pair of DTF signals, where the difference signal has positive and negative values about a zero crossing axis which are representative of transmittivity relative to wavelength and where a resulting shift in the location of the difference signal at the zero crossing axis represents a changing refractive index of the dielectric at the metal-dielectric interface. 
 
     
     
       6. The sensor of  claim 5  wherein the sensor operates in a closed loop configuration. 
     
     
       7. The sensor of  claim 6  wherein the processor means obtains the DTF signals at FWHM (Full Width Half Maximum) values. 
     
     
       8. The sensor of  claim 7  where the array sample is a grating array. 
     
     
       9. The sensor as in  claim 8  where the laser means includes a laser for generating a range of tunable laser beams and beam splitter means for generating the pair of collimated laser beams. 
     
     
       10. The sensor as in  claim 9  including detector means for obtaining the DTF signals. 
     
     
       11. The sensor as in  claim 10  including a computer for calculating the difference signal. 
     
     
       12. A surface plasmon resonance sensor operating in a closed loop configuration and having a metal-dielectric interface formed by microfluidic channels integrated with metal-dielectric layer chips, the sensor comprising:
 laser means for generating and imaging a pair of collimated laser beams at different angles of incidence onto substantially the same spot on a metal nanohole grating array sample at the metal-dielectric interface to excite surface plasmons on the array sample and forming a pair of parallel laser beams emerging from the array sample; 
 processor means for obtaining a pair of device transfer function (DTF) signals at FWHM (Full Width Half Maximum) values from the pair of parallel laser beams, where each respective DTF signal has a different angle of incidence and an intensity peak at a different wavelength relative to a reference wavelength and for calculating a difference signal from the pair of DTF signals, where the difference signal has positive and negative values about a zero crossing axis which are representative of transmittivity relative to wavelength and where a resulting shift in the location of the difference signal at the zero crossing axis represents a changing refractive index of the dielectric at the metal-dielectric interface. 
 
     
     
       13. The sensor of  claim 12  where the processor means includes a pair of detectors and where the pair of parallel laser beams impinge on the pair of detectors. 
     
     
       14. The sensor of  claim 12  where the pair of collimated laser beams are transmitted through the grating array sample. 
     
     
       15. The sensor of  claim 12  where the pair of collimated laser beams are reflected from the grating array sample. 
     
     
       16. The sensor of  claim 12  including means for detecting the differential intensity of the pair of parallel laser beams.